[FE] Add modal-footer to pipeline security tab vulnerabilities modal

Why are we doing this work

NOTE: This issue is dependent on #300753 (closed) and the description is written assuming that it is already merged.

Previously, the pipeline security tab used a Vuex version of the vulnerability list. When an item was clicked on the list, a modal pops up that shows details about the vulnerability:

Now that we've switched to the GraphQL version of the vulnerability list, we need to show the same modal using the ee/app/assets/javascripts/vue_shared/security_reports/components/vulnerability_details.vue component:

Here's a screenshot that visually divides the modal into three parts. This is just a suggestion that we could follow in order to deliver this task iterately:

Relevant links

Issue Breakdown

Part 1	#300755 (closed)
Part 2	#337488 (closed)
Part 3	👈 This issue
Part 4	#337873 (closed)

Other

Epic	&4969 (closed)
Design issue	#227105 (closed)
Backend issue	#298760 (closed)

Non-functional requirements

• Documentation: screenshots need to be updated and text modified if necessary
• Testing: tests need to be updated

Implementation plan

• TBD